Question: Solve for $x$ and $y$ using substitution. ${2x+y = -3}$ ${x = -2y-12}$
Solution: Since $x$ has already been solved for, substitute $-2y-12$ for $x$ in the first equation. ${2}{(-2y-12)}{+ y = -3}$ Simplify and solve for $y$ $-4y-24 + y = -3$ $-3y-24 = -3$ $-3y-24{+24} = -3{+24}$ $-3y = 21$ $\dfrac{-3y}{{-3}} = \dfrac{21}{{-3}}$ ${y = -7}$ Now that you know ${y = -7}$ , plug it back into $\thinspace {x = -2y-12}\thinspace$ to find $x$ ${x = -2}{(-7)}{ - 12}$ $x = 14 - 12$ ${x = 2}$ You can also plug ${y = -7}$ into $\thinspace {2x+y = -3}\thinspace$ and get the same answer for $x$ : ${2x + }{(-7)}{= -3}$ ${x = 2}$